The data for the mean sea-levels at Izmir, during the period of 22 years from 1937 to 1958, were taken from Publication Scientifique, Monthly and Annual Mean Heights of Sea Levels. The investigation was made with the intention of finding some evidence, if any, for the existence of abnormally large changes in the heights rof yearly mean sea-levels, preceding the great earthquakes similarly as in the cases of Kwanto Earthquake 1923, Niigata Earthquake 1964, and of others in Japan as well as of Lisbon Earthquake 1941 in Portugal concerning the problem of predicting the occurrence of great earth-quakes. The data for the great earthquakes, with magnitudes greater than 7.0, and epi-central distances less than 600 km, were taken from the Scientific Chronological Table similarly treated as in the case of Lisbon in Portugal, having no data for sea water density and barometric pressure at hand.

View full abstract

The author makes an attempt to establish a one-to-one mathematical relationship between the gravity field and the mantle convection currents in two-dimensional models. It is presumed that an up-coming convective flow produces a high gravity anomaly, on the other hand a low anomaly is caused by a down-going flow. The set of differential equations governing the steady-state convective motion is solved to obtain the density disturbances and the corresponding streamlines. Applying the solution to the satellite gravity anomaly, the author discusses the convective flow supposed to go down along the Japan Arc.

View full abstract

The simultaneous observation of artificial satellites is one of the most powerful means for connecting the distant geodetic datum stations or the triangulation nets. Through these observations, the direction and distance between two stations are first determined and then world-wide frame work connecting all the observation points is constructed. In these work, large quantity of the observational data which is not always coincident one another must be dealt with, and some adjustment is necessary. In this adjustment, three dimensional consideration is required because the observation stations are distributed globally and it is impossible to apply the two dimensional model to these stations. In this paper, the writer treats a method of the three dimensional adjustment. This method corresponds essentially to solve the observational equations applying the method of least square and this is equally applicable for the data of direction observation and of range measurement of the satellites. This adjustment will be useful for the determination of accurate posion of Japanese datum referred to other datum points and the construction of large triangulation net including the long base lines in Japan.

View full abstract

The general description of the TEM tiltmeter has been already presented [1]. In the present paper, details of the electronic devices of the instrument is introduced, which consist of the following four sections, 1) differential transformer as a transducer, 2) exciter of the differential transformer and amplifie, 3) power-supply and4) recorder and reset circuit, The author's intention of designing the electronic devices is as follows:1) The life time should be as long as possible.2) Electronic parts should be easily obtained at the market.3) Repairing time should be as short as possible. It has beea cleared that MTBF (mean time between failures) of the present electronic circuits, shown on the Weibull distribution paper, is only 4 years.

View full abstract

Water-tube tiltmeter observations have been conducted at the Aburatsubo Crustal Movement Observatory since 1949. The present paper reviews the data accumulated in the past twenty years in order to examine if the station observation of this type can monitor the crustal movements satisfactorily or not. The Miura Peninsula area, in which the Aburatsubo station is located, is particularly suitable for this purpose, because the G. S. I's data of frequent relevelling and of mareographic observation are available for comparison. Following are the conclusions thus obtained: (i) Gradual westward tilting of the ground, which was recorded at Aburatsubo for the peiriod 1949-1960, turn to active eastward tilting about 1961. The basic mode of this movements, particularly the active eastward tilting since 1961, is witnessed by the levellings in the southern part of the peninsula. Similar mode of land movements is also noticed on the mareographic records at Aburatsubo and Mera as well as on the tiltmeter record at Nokogiriyama, where the latter two stations are located at an adjacent peninsula. (ii) As to the detailed features, however, tiltmeter data do not agree with the geoditic data necessarily. The writer can hardly explain the causes of disagreement, but he tenta-tively considers that it might be attributed partly to sea level anomalies which result in local tilting of the coastal ground by loading.

View full abstract

In relation to the research of the present crustal movemont in the South Kanto District, the records of the retriangulation made soon after the Great Kanto Earthquake of 1923 have been reanalized. The horizontal movement derived by the present analysis is well accordant with other observed facts, such as the vertical movement discovered by the re-leveling. The crustal movement associated with the earthquake is estimated to have resulted from a shallow dip thrust faulting with large lateral slip. From the amount of the horizontal displacement near the fault plain, the dip of the fault is estimated as 25°-40° in NE direction. The strain change of the earth's crust at the time of the earthquake shows that the crust in the source region had been compressed toward north-south before that time.

View full abstract

Measurements of vertical gradient of gravity carried out at Keio Plaza Hotel Building which was built recently. This building is in Tokyo (latitude: 35°41.2'E longitude: 139°41.9'N) and its height is about 170 m above the ground. The mean value of the gradient measured was 0.3049 mgal/m ± 0.00032SD. There are four stations where the vertical gradients of gravity have been measured in and around Tokyo. The distribution has a tendency to increase toward north in this area same as the free air anomaly distribution.

View full abstract